地震强度因子M_f值在华北中强以上地震前的短期异常变化

THE SHORT-TERM ANOMALY VARIATION OF SEISMIC MAGNITUDE FACTOR M_f-VALUE BEFORE MODERATE OR STRONG EARTHQUAKES IN NORTH CHINA

使用华北地区1972～1992年的中小地震震级资料进行地震强度因子均值空间扫描，研究华北地区中强以上地震前的短期异常变化。结果表明，在震前0．5a左右的短期阶段，Mf值中期异常区存在二类不同形态的变化，其中大部分震例的Mf值中期异常区出现明显的缩小乃至消失，可将这一特征作为短期异常的标志；而另一部分展例的中期异常区无明显变化。文中讨论了Mf值用于短期地震预报的方法和预报效果，并对峙值的短期变化过程进行了定性的物理解释。

The magnitude data of moderate or small earthquake during 1972~ l992 in NorthChina are used for spatial scanning of seismic magnitude factor Mf-value in thispaper. The short-term anomaly variation before moderate or strong earthquakes is stu-died. The result shows that within the short-term, about half a year before strongearthquakes, there are two different types of variations in the mid-term anomaly zone ofMf-value. In most of earthquake cases the mid-term anomaly zone is obviously reducedor disappeared. We regard this feature as the mark of the short-term anomaly. However,in some earthquake cases the mid-term anomaly zone has no obvious variation. Theproblems of how to use the Mf-value in the short-term earthquake prediction and howwell the prediction effect is, and the qualitative physical interpretation of Mf-valueanomaly variation are also discussed.